High vacuum discharge tube for high voltages



Jan. 20, 1970 K. FRANKE ETAL 3,491,232

HIGH VACUUM DISCHARGE TUBE FOR HIGH VOLTAGES Filed Aug. 23, 1967 Fig-IFi .2

INVENTORS KURT FRANKE Y KURT HIRSCH United States Patent M 3,491,232HIGH VACUUM DISCHARGE TUBE FOR HIGH VOLTAGES Kurt Franke and KurtHirsch, Hamburg, Germany, assignors, by mesne assignments, to US.Philips Corporation, New York, N.Y., a corporation of Delaware FiledAug. 23, 1967, Ser. No. 662,598 Claims priority, application Germany,Aug. 27, 1966, P 40,278 Int. Cl. H01j 1/53 US. Cl. 313240 6 ClaimsABSTRACT OF THE DISCLOSURE The invention relates to a high vacuumdischarge tube for high voltages comprising an anode cylinder having atleast one open end and inside the cylinder an anode surface arrangedperpendicular to the cylinder axis and furthermore comprising a cathodeplaced outside the cylinder and being surrounded by screening means,said screening means having an opening provided with screening surfaces,and located at some distance opposite the open end of the anodecylinder.

In some known high vacuum discharge tubes screens are provided toprevent surface charges being formed on the wall of the vessel and alsoto prevent primary or secondary electrons from leaving the cathode-anodespace unintentionally.

Such discharge tubes have a cathode or electron emitting filament placedinside a generally cylindrical anode. However, the known screening meansare not suitable for high vacuum discharge tubes for high voltages asthese tubes are exposed to temperatures which require screening means ofa particular type. With the known means an effective screening cannot berealized.

In high vacuum rectifier tubes in particular for high and very highvoltages, screening means are known which surround a cylindrical anodeat such a distance, that the anode surfaces exposed to electronbombardment are situated inside the screening cup.

These screening means are intended to prevent charged carriers escapingfrom the active discharge space and thus can no longer reach the wall ofthe vessel which otherwise would cause in the long run a brownishdiscoloring of the glass.

The so-called ballast tubes as presently available also show thisbrownish discoloring. These ballast tubes are used in color televisionreceivers in which they are connected in parallel with the colourpicture tube in order to keep constant the sum of the currents throughthe picture tube and the ballast tube. This is an essential function asotherwise the colors will not be reproduced correctly. The ballast tubesare triodes, which show as soon as they are switched on fluorescence ofthe glass wall which disappears when the tube has been in operation fora longer time and then changes into a brownish discoloring of the glass.It appears that the discoloring results from a decomposition of the leadoxide contained in the glass. The higher the operating voltage of thetube,

3,491,232 Patented Jan. 20, 1970 the greater is the decomposition of thelead oxide and this will finally result in the destruction of the glassvessel.

As already mentioned the anode surfaces of these high vacuum dischargetubes for high voltages are situated inside an anode cylinder such thatthe anode surfaces, viewed in the direction of the electron stream, liedeep in the cylinder. Thus, it is unlikely, that secondary electrons setfree at the anode by the bombarding primary electrons, can leave theanode cylinder in a direction opposite to the direction of motion of theprimary electron stream and can arrive at the glass wall. The problemunderlying the invention was first of all to establish the physicalphenomena leading to the brownish discoloring of the glass of theballast tubes. As a result of measurements the inventors found, that atvery high voltages a radio-active radiation is set free by the electronbombardment of the anode surface situated deep in the anode cylinder.This radiation strikes the surfaces of the cathode screening means andliberates at these surfaces primary electrons which can travel to andreach the glass wall unhindered. This phenomenon has up to now not beenobserved in electron tubes of the type mentioned. Therefore according tothe invention there are provided in a high vacuum discharge tube forhigh voltages of the above-mentioned type screening means such thatphotoelectrons, liberated at the screening surfaces by radio-activeradiation emanating from the anode surface and produced by electronbombardment of that surface situated rather deep inside the anodecylinder, are prevented from reaching the wall of the vessel and areforced to return to the anode cylinder.

According to the invention the screening means may consist of a cupfixed to the cathode screening means and provided with a current supplylead, said cup surrounding the anode cylinder up to a certain height andalso surrounding the space between the cylinder and the screeningsurfaces. The cup itself may be provided with a supply lead leading tothe outside of the tube. Alternatively, according to the invention, thecup may be electrically connected to the cathode screening means whichresults in a simpler construction.

In many cases it is suflicient to use as screening means according tothe invention, a metal ring adjacent to the tube wall, and to providethe ring with supply lead leading to the outside of the tube. Accordingto the invention this metal ring is fixed to the cathode screening meansand is electrically connected thereto. Moreover it is possible toconnect the cathode screening means to the cathode of the tube in thesame way as it is done in known tubes. At variance with knownarrangements according to the invention not only is the anode screenedbut all surfaces of the discharge system which might be exposed to theradioactive radiation and which in consequence thereof could give offphotoelectrons proceeding to the wall of the tube.

The drawing shows several embodiments of the invention which will beexplained hereafter.

In the drawing:

FIGURE 1 shows, partly in a cross-sectional view, a ballast tube forcolor television receivers provided with a screening cup according tothe invention.

FIGURE 2 shows likewise a ballast tube for colour television receiversprovided with a metal screening ring according to the invention.

In FIGURES 1 and 2 the glass vessel of the tube is designated by thenumeral 1. An anode cap 2, fused in the glass wall and projecting fromthe outside of the tube, carries an anode-cylinder 5 by means of asupport 3 and supporting rods 4. Inside this anode cylinder andperpendicular to its axis is situated a cup shaped body 6 having ananode surface 7.

At the bottom of the .tube and standing thereon is arranged a cathode 8surrounded by a grid 9; both are placed inside a cathode screen 10. Thescreen 10 has an opening 11 through which the electrons emitted by thecathode 8 after having passed the grid '9 can proceed to the anodecylinder 5. These electrons are accelerated by a voltage of about 25,000volts applied between the anode cylinder and the cathode 8 and hit at avery high speed the anode surface 7. This electron bombardment sets freea radioactive radiation which is emitted in the direction to thecathode. This radiation indicated by the dotted line 12 reaches thesurface 13 of the cathode screen and there sets free photoelectronswhich leave the surface for instance as indicated by the dotted line 14.In tubes of the known types the photoelectrons would reach the glasswall 1 unhindered. According to the invention there is arranged ascreening cup 15 such that the electrons 14 set free by the radioactiveradiation travel in the direction of the dotted line 16, that is to sayin the direction to the anode and consequently are prevented fromreaching the glass wall. The lifetime of ballast tubes provided withsuch a screening cup is substantially longer than the lifetime of thetubes hitherto known.

Plates 17 are arranged in order to reflect heat radiation. Furthermorethe tube is provided with contact-pins 18.

In the embodiment according to FIGURE 2 a .metal ring 19 adjacent thetube wall 1 is used instead of the screening cup. The ring is connectedby means of a lead 20 to the cathode screen 10 and also to the cathode 8such that both the ring and the screen 15 modify the course of theequipotential lines, thereby forcing the photoelectrons to turn back andpreventing them from traveling to the glass wall.

What is claimed is:

1. A high vacuum discharge tube for high voltages comprising anevacuated envelope and within said envelope an anode cylinder having atleast one open end and inside the cylinder an anode surface arrangedperpendicular to the cylinder axis a cathode placed outside thecylinder, screening means surrounding the oathodes, said cathodescreening means having an opening provided with screening surfaces andlocated spaced from and opposite the open end of the anode cylinder,additional screening means surrounding the open end of said anodebetween said envelope and said cathode screening means for interceptingphotoelectrons liberated at the said 4 screening surfaces by radioactiveradiation emanating from the anode surface and produced by electronbombardment of that surface situated within the anode cylinder, andmeans to apply a potential to said latter screening means for returningthe photoelectrons to the anode cylinder.

2. A high vacuum discharge tube according to claim 1 Where theadditional screening means comprise a cup fixed to the cathode screeningmeans and provided with a current supply lead, said cup surrounding theanode cylinder up to a certain height and also surrounding the spacebetween the cylinder and the screening surfaces.

3. A high vacuum discharge tube according to claim 2, wherein thescreening cup is electrically connected to the cathods screening means.

4. A high vacuum discharge tube according to claim 1 wherein theadditional screening means comprise a metal ring adjacent the tube wall,said ring being provided with a current supply lead.

5. A high vacuum discharge tube according to claim 4, wherein the metalring is fixed to the cathode screening means and is electricallyconnected thereto.

6. A high vacuum discharge tube according to claim 1 wherein theadditional cathode screening means are electrically connected to thecathode.

References Cited UNITED STATES PATENTS 2,040,883 5/1936 Solomon 313313 X2,464,270 3/ 1949 Spencer 3 l33 13 X 2,888,590 5/1959 Taylor 3l32992,933,633 4/ 1960 Spicer et a1 313-313 3,041,494 6/1962 Lough et a13l3285 3,231,778 1/1966 Allgaier 3133l3 FOREIGN PATENTS 1,106,979 7/1955 France.

OTHER REFERENCES R.C.A. Technical Notes by DeMuro et al. No. 137.

JOHN W. HUCKERT, Primary Examiner ANDREW J. JAMES, Assistant ExaminerUS. Cl. X.R.

CERTIFICATE OF CORRECTION PatentNo. 3491232 Dated January 20, 1970Inventofls) KURT FRANKE and KURT n'mscn It is certified that errorappears in the above-identified patent and that said Letters Patent arehereby corrected as shown below:

Col. 3, line 10, after "emitted" insert -perferenti ally-- Signed andsealed this 14thday of July 1970 U Alma Edward M. Fletcher, Ir.

mm E. SOHUYLIR, JR- Attcsung Officer Commissioner of Patents

